fixing init.md documentation to not require rpcpassword
fixing init.md documentation to not require rpcpassword

Summary: This is a backport of Core [[https://github.com/bitcoin/bitcoin/pull/18157 | PR18157]]

Test Plan: Proof-reading

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D8964

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